NASA said today it has reached a “significant milestone” in a project to create an ultra-quiet supersonic passenger jet. The space agency has completed a preliminary design review of its QueSST aircraft concept and found that it is capable of fulfilling objectives for what NASA calls “Low Boom Flight Demonstration,” which basically means it should be able to fly at supersonic speeds without that noisy sonic boom. As NASA describes it, the airplane will just make a soft “thump,” which I’m guessing is more pleasant.

Last year, NASA teamed up with aerospace defense giant Lockheed Martin on the experimental project. Now that the design review is complete, NASA says the next step is to start soliciting proposals to actually build the thing. It expects to award a contract early next year with the hope that flight testing could begin by 2021. Check out more on the project here.